This invention relates generally to methods and apparatus for radiation imaging systems and, more particularly, to methods and apparatus for combating cone beam artifacts utilizing weighted generalized helical interpolation.
In multislice computed tomographic (CT) imaging systems, a detector array is segmented so that a plurality of parallel or quasi-parallel slices of projection data are acquired and processed to construct a plurality of images corresponding to several slices though a volume. A range of pitches exists for which measurements are available at least at two source locations. Measurements acquired at different source positions are known as xe2x80x9cconjugate measurements.xe2x80x9d Pitches for which conjugate measurements are available are known as xe2x80x9cHigh Qualityxe2x80x9d (HQ) pitches. When an HQ pitch is used, a CT imaging system (or xe2x80x9cscannerxe2x80x9d) is said to operate in xe2x80x9cHQ mode.xe2x80x9d For a four-slice scanner, the helical pitch of the HQ mode is 3:1. An eight-slice scanner enables higher pitch modes to be used. A natural pitch selection for an eight-slice scanner is thus in the range of 5:1 to 7:1, to increase the volume coverage of a patient or object being imaged. However, because of increased cone-beam artifacts, it is difficult to maintain image quality when using higher pitch modes with known reconstruction methods and apparatus.
There is therefore provided, in one aspect of the present invention, a method for reconstructing at least one image representative of an object with a scanning imaging system having a multislice detector array and a radiation source configured to emit a radiation beam through the object and towards the multislice detector array, the multislice detector array having a plurality of detector elements arranged in a plurality of detector rows. The method includes helically scanning the object with the scanning imaging system to acquire a plurality of projection views of the object, including projection views acquired at different cone angles of the radiation beam; selecting a region of reconstruction (ROR) to define sets of conjugate samples in the projection views; and reconstructing at least one image of the object, the reconstruction including weighting the sets of conjugate samples using a cone-angle dependent weighting function, and filtering and backprojecting the weighted samples.
In another aspect, the invention provides a method that includes helically scanning the object with the scanning imaging system to acquire a plurality of projection views of the object, including projecting views acquired at different cone angles of the radiation beam, selecting an ROR to define sets of conjugate samples in the projection views; and reconstructing at least one image of the object, the reconstruction including weighting the sets of conjugate samples using a cone-angle dependent weighting function, and filtering and backprojecting the weighted samples, the weighting including applying a detector row k dependent scaling factor wk that scales linearly and inversely with the cone angles.
In yet another aspect, the present invention provides a scanning imaging system for reconstructing at least one image representative of an object, the scanning imaging system including a multislice detector array, a radiation source configured to emit a radiation beam through an object to be imaged and towards the multislice detector array, the multislice detector array having a plurality of detector elements arranged in a plurality of detector rows. The scanning imaging system is configured to: helically scan the object to be imaged to acquire a plurality of projection views of the object, including projection views acquired at different cone angles of the radiation beam; select an ROR to define sets of conjugate samples in the projection views; and reconstruct at least one image of the object, wherein to reconstruct the at least one image, the multislice imaging system is configured to weight the sets of conjugate samples using a cone-angle dependent weighting function, and to filter and backproject the weighted samples.
In still another aspect, the present invention provides a scanning imaging system for reconstructing at least one image representative of an object, the scanning imaging system including a multislice detector array, a radiation source configured to emit a radiation beam through an object to be imaged and towards the multislice detector array, the multislice detector array having a plurality of detector elements arranged in a plurality of detector rows. The scanning imaging system is configured to; helically scan the object to be imaged to acquire a plurality of projection views of the object, including projection views acquired at different cone angles of the radiation beam; select an ROR to define sets of conjugate samples in the projection views; and reconstruct at least one image of the object, wherein to reconstruct the at least one image, the multislice imaging system is configured to weight the sets of conjugate samples using a cone-angle dependent weighting function, and to filter and backproject the weighted samples, wherein to weight the conjugate samples, the scanning imaging system is configured to apply a detector row k dependent scaling factor wk that scales linearly and inversely with said cone angles.
In another aspect, the present invention provides a processor for reconstructing at least one image representative of an object helically scanned by a scanning imaging system. The processor is configured to: input a plurality of projection views of a scanned object, including projection views acquired at different cone angles of a radiation beam by a multislice detector array having a plurality of detector rows; select an ROR to define sets of conjugate samples in the projection views; and reconstruct at least one image of the object, wherein to reconstruct the at least one image, the processor is configured to weight the sets of conjugate samples using a cone-angle dependent weighting function, and to filter and backproject the weighted samples.
In yet another aspect, the present invention provides a processor for reconstructing at least one image representative of an object helically scanned by a scanning imaging system. The processor is configured to: input a plurality of projection views of a scanned object, including projection views acquired at different cone angles of a radiation beam by a multislice detector array having a plurality of detector rows; select an ROR to define sets of conjugate samples in the projection views; and reconstruct at least one image of the object, wherein to reconstruct the at least one image, the processor is configured to weight the sets of conjugate samples using a cone-angle dependent weighting function, and to filter and backproject the weighted samples, wherein to weight the sets of conjugate samples, the processor is configured to apply a detector row k dependent scaling factor wk that scales linearly and inversely with the cone angles.
In still another aspect, the present invention provides a computer readable medium having encoded thereon instructions interpretable by a computer to instruct the computer to: input a plurality of projection views of a scanned object, including projection views acquired at different cone angles of a radiation beam by a multislice detector array having a plurality of detector rows; select an ROR to define sets of conjugate samples in the projection views; and reconstruct at least one image of the object, wherein to reconstruct the at least one image, the process is configured to weight the sets of conjugate samples using a cone-angle dependent weighting function, and to filter and backproject the weighted samples.
In still another aspect, the present invention provides a computer readable medium having encoded thereon instructions interpretable by a computer to instruct the computer to: input a plurality of projection views of a scanned object, including projection views acquired at different cone angles of a radiation beam by a multislice detector array having a plurality of detector rows; select an ROR to define sets of conjugate samples in the projection views; and reconstruct at least one image of the object, wherein to reconstruct the at least one image, the process is configured to weight the sets of conjugate samples using a cone-angle dependent weighting function, and to filter and backproject the weighted samples, wherein to instruct the computer to weight the sets of conjugate samples, the computer-readable medium has encoded thereon instructions configured to instruct the computer to apply a detector row k dependent scaling factor wk that scales linearly and inversely with the cone angles.
The above-described embodiments of the present invention reduce cone-beam artifacts in reconstructed images, thus providing increased imaging coverage while maintaining high image quality.